The use of screw conveyors for elevating dry granular or powdery substance from one level to another is well known for many applications. The screw construction usually consists of a central rigid rotating shaft with helical flighting strips welded thereto, with shaft bearings suitably mounted at the upper and lower extremities of the shaft, and the whole enclosed in a usually cylindrical housing which is in reasonably close proximity to the outer edge of the helical flighting strips. An inlet opening is provided in one side of the housing near the lower end of the assembly, and an outlet opening is provided near the top. The details of flighting pitch, numbers of flights, screw rotating speed, angle of inclination of the shaft, and the like, may be varied considerably and are unimportant to this disclosure.
In many applications, the screw conveyor housing may be an integral pipe, with no joints except those necessary for fabrication and erection. In some applications, however, the housing must be opened at least daily for inspection and thorough cleaning. One such application is on large breading machines which coat food products with breading material. These machines supply a large excess of breading material around the pieces to be coated, thus insuring full coating of the pieces, and thus requiring that the excess be returned to an elevated hopper for re-use. A vertical or nearly vertical screw conveyor performs the elevating function on the excess breading material.
When a vertical screw conveyor is used on a food processing machine as above, government regulations require that it be cleaned after each day's operation, and all internal surfaces must be exposed for visual inspection. This requires longitudinal joints in the housing to permit opening of about fifty percent of the housing circumference, and transverse joints at top and bottom of the removable section. These joints are the focus of this invention.
The manufacturer of breading machines, who seldom has a production run exceeding 10 machines at one time, and usually works with stainless steel only, must keep his construction cost as low as possible, therefore his fabrication technology for these joints is pretty much limited to simple sheet metal technique such as bending, punching, and welding. The purchasers of these machines who must pay a high dollar figure for them due to short production runs, understandably object when the vertical conveyor joints leak expensive breading onto the floor, yet they will also object to additional cost for leak-proof joints.
In prior art practice, the longitudinal joints of such a housing in food machines are most frequently in a plane which also contains the rotating axis of the screw. An outwardly extending flange on each side of each housing half is formed to lie in the above plane, and various clamping or bolting arrangements are used to hold the flanges together. One side may be hinged to permit the movable housing half to swing open. Some modifications may be made to this arrangement, but the sealing joint remains essentially the same, two planar strips in the same plane which must be well mated to seal, and are held in fixed relation by a piano type hinge or by a multitude of clamps or bolts.
These present joint configurations are frequently less than satisfactory for a number of reasons. Piano hinges are unsanitary, are subject to unadjustable wear, and are easily warped to negate tight closure. The requirement for many clamps means the joint is inherently leaky, and will leak unless all clamps are perfectly adjusted. Joints using a multitude of loose bolts are abhorrent to the purchaser because it is axiomatic that totally removable components will be lost during cleanup. When joint members begin to degrade after use, breading losses become quite expensive both in dollar value of the breading and in frequent floor cleaning operations necessary. Gasketed joints are discouraged by government regulatory agencies because of the inherent porosity of most suitable gasket materials, and the danger of loose gasket pieces entering the food product. Machined joints of heavy material are prohibitively expensive. Thus, it may be seen that a more reliable yet still economical longitudinal joint would be appreciated by the users of large breading machines and possibly by other machine users.